Xamarin 表单选择器确定或取消按钮按下检测

Posted 2023-03-25

【中文标题】Xamarin 表单选择器确定或取消按钮按下检测

【英文标题】：Xamarin Forms picker OK or Cancel button pressed detection

【发布时间】：2019-09-01 20:42:13

【问题描述】：

我正在使用 Xamarin Forms 开发应用程序。我的选择器组件有一些问题。

用 Picker 拾取后，需要判断是按下 OK 还是 Cancel 按钮。

我尝试了 Focus 和 Unfocus，但它不能帮助我确定哪个用户正在按下 OK 或 Cancel 按钮。

【问题讨论】：

建议您制作一个自定义渲染器，然后创建在这些事件触发时通知您的本机处理程序

如何在这个主题上使用自定义渲染器？我需要将它用于 ios 和 android。我无法使用自定义渲染器捕获 OK 或 Cancel 按钮的点击事件。

您可以查看我的回答。如果我的回答对您有帮助，请不要忘记标记，以便更多人看到。

【参考方案1】：

解决方案：

你应该在CustomRenderer中重写Picker的工具栏

iOS

[assembly:ExportRenderer(typeof(Picker),typeof(MyPickerRenderer))]
namespace App6.iOS

  public class MyPickerRenderer:PickerRenderer
  
    public MyPickerRenderer()
    

    



    protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
    
        base.OnElementChanged(e);

        if(Control!=null)
        



            UIPickerView pickerView = (UIPickerView)Control.InputView;


            // get the button Done and rewrite the event
            UIToolbar toolbar = (UIToolbar)Control.InputAccessoryView;

            UIBarButtonItem done = new UIBarButtonItem("OK", UIBarButtonItemStyle.Done, (object sender, EventArgs click) =>
            

                MessagingCenter.Send<Object>(this,"Ok_Clicked");

            );

            UIBarButtonItem cancel = new UIBarButtonItem(UIBarButtonSystemItem.Cancel, (object sender, EventArgs click) =>
            

                MessagingCenter.Send<Object>(this, "Cancel_Clicked");
            );


            UIBarButtonItem empty = new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace, null);

            toolbar.Items = new UIBarButtonItem[]  cancel,empty, done ;
        

    
  

安卓

[assembly: ExportRenderer(typeof(Picker), typeof(MyPickerRenderer))]
namespace App6.Droid

  public class MyPickerRenderer : PickerRenderer
  
    IElementController ElementController => Element as IElementController;

    public MyPickerRenderer(Context context) : base(context)
    

    


    private AlertDialog _dialog;

    protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
    
        base.OnElementChanged(e);

        if (e.NewElement == null || e.OldElement != null)
            return;

        Control.Click += Control_Click;
    

    protected override void Dispose(bool disposing)
    
        Control.Click -= Control_Click;
        base.Dispose(disposing);
    




    private void Control_Click(object sender, EventArgs e)
    

        Picker model = Element;

        var picker = new NumberPicker(Context);
        if (model.Items != null && model.Items.Any())
        

            picker.MaxValue = model.Items.Count - 1;
            picker.MinValue = 0;

            picker.SetDisplayedValues(model.Items.ToArray());

            picker.WrapSelectorWheel = false;
            picker.Value = model.SelectedIndex;
        

        var layout = new LinearLayout(Context)  Orientation = Orientation.Vertical ;
        layout.AddView(picker);

        ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, true);

        var builder = new AlertDialog.Builder(Context);
        builder.SetView(layout);

        builder.SetTitle(model.Title ?? "");
        builder.SetNegativeButton("Cancel  ", (s, a) =>
        
            MessagingCenter.Send<Object>(this, "Cancel_Clicked");
        );
        builder.SetPositiveButton("Ok ", (s, a) =>
        
            ElementController.SetValueFromRenderer(Picker.SelectedIndexProperty, picker.Value);
            // It is possible for the Content of the Page to be changed on SelectedIndexChanged.
            // In this case, the Element & Control will no longer exist.
            if (Element != null)
            
                if (model.Items.Count > 0 && Element.SelectedIndex >= 0)
                    Control.Text = model.Items[Element.SelectedIndex];
                ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
                // It is also possible for the Content of the Page to be changed when Focus is changed.
                // In this case, we'll lose our Control.

            
            MessagingCenter.Send<Object>(this, "Ok_Clicked");
        );

        _dialog = builder.Create();
        _dialog.DismissEvent += (ssender, args) =>
        
            ElementController?.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
        ;
        _dialog.Show();
    

  

您可以使用 MessagingCenter 处理表单中的事件。

在内容页面中

public MainPage()

   InitializeComponent();

   MessagingCenter.Subscribe<Object>(this, "Ok_Clicked", (sender)=> 

      picker.Unfocus();

      DisplayAlert("Title", "Ok has been clicked", "cancel");

      //do something you want

   );

   MessagingCenter.Subscribe<Object>(this, "Cancel_Clicked", (sender) => 

       picker.Unfocus();

       DisplayAlert("Title", "Cancel has been clicked", "cancel");

       //do something you want
     );